The present invention relates to improvements in a track rail of a linear motion rolling guide unit for linearly rolling to guide a slider with balls therebetween, in which the track rail is a substantially rectangular columnar and is formed with an arcuate raceway groove partly on the longitudinal wall surface thereof and the slider has a substantially U shaped section with angles and is formed with an arcuate raceway groove on an inner peripheral surface thereof opposed to the raceway groove of said track rail.
Heretofore, a track rail of a conventional linear motion rolling guide unit of this type as shown in FIG. 6 has been known.
The conventional track rail shown in FIG. 6 has an upper flat surface 10 and a bottom mounting portion 11 formed in parallel with one another. Load ball grooves 12 and 13 are formed at predetermined positions for supporting and guiding a slider with balls. The track rail has lower side surfaces 14 and 15 formed perpendicularly to the bottom thereof. A relieved groove 16 is formed axially at a predetermined position of the bottom mounting portion 11. The track rail is formed with a mounting hole 17 passing through the upper flat surface 10 and the bottom mounting portion 11. The relieved groove 16 formed at the bottom mounting portion 11 of the track rail reduces an area of grinding to decrease a machining cost thereof and to facilitate the formation of a right angle at both side surfaces at the time of mounting.
However, the track rail of the conventional linear motion rolling guide unit has the following disadvantages.
First, when the conventional track rail is clamped at predetermined positions of a bed of a machine tool with bolts, since the diameter D.sub.0 of the mounting hole is smaller than the size H.sub.0 of the mounting portion, the portion completely clamped at the opposed mounting surface and the portion incompletely clamped thereat occur according to the clamping degrees of the bolts, and the track rail cannot be mounted in parallel with the bed.
Second, when the clamping forces of the bolts are increased in the conventional track rail, a difference of clamping forces of the bolts occurs according to the elongating degree of the bolts and the bending degree of the track rail, and the track rail cannot be mounted in parallel with the bed.